Turbine wheel



ril 4, 1967 Original Filed June 29, 1964 G. D. CHANDLEY TURBINE WHEEL 2 Sheets-Sheet 1 April 4, 1967 G. D. CHANDLEY 3,312,449

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United States Patent Ofiice 3,312,449 Patented Apr. 4, 1967 3,312,449 TURBINE WHEEL George D. Chandley, Alliance, Ohio, assignor to TRW Inc., a corporation of Ohio Original application June 29, 1964, Ser. No. 378,643, now Patent No. 3,283,377, dated Nov. 8, 1966. Divided and this application July 20, 1966, Ser. No. 566,607

6 Claims. (Cl. 253-77) This application is a division of my copending application Ser. No. 378,643, filed June 29, 1964 now Patent No. 3,283,377, dated Nov. 8, 1966.

The present invention is directed to an improved turbine wheel for jet engines and the like.

One of the limiting factors in the design of any turbine has been the ability of the turbine wheel to Withstand the conditions of temperature and stress existing during operation of the engine. Turbine wheels in particular must be capable of withstanding dynamic loads under high stress conditions and have satisfactory creep characteristics at elevated temperatures. Substantial advances have been made in the chemistry of alloys used for turbine wheels, with the result that permissible turbine inlet temperatures have increased, thereby marked increasing the net output and the cycle efficiency of the engine.

Control of the chemistry of the alloy, however, is not alone sufficient to provide an optimum solution to the problem. Different portions of the turbine wheel are subjected to different kinds of stresses, in different amounts. The present invention provides a structure which has the proper grain characteristics in various portions of the wheel which are best suited to resist the particular stresses which that portion of the structure is to encounter during use.

It would be highly desirable if a turbine wheel could be manufactured as a cast integral structure. However, exist-ing technology for the production of cast turbine Wheels is deficient in that it has not been possible to cast an equiaxed grain size in the thin air foil sections of the wheel and, at the same time, produce sound, equiaxed grain size in the heavier, hub section of the wheel. The present invention overcomes this problem, and provides a cast turbine wheel having thick and thin sections of equiaxed, sound structure having greatly improved ductility properties.

An object of the present invention is to provide an improved cast, integral turbine wheel structure in which the grain configuration is substantially identical throughout the casting but the grain sizes vary at different portions thereof.

Another object of the invention is to provide a cast, integral turbine wheel which has substantially improved ductility properties.

The turbine wheel of the present invention has a geometry which is standard, in that it contains a relatively massive hub section, a wheel portion extending annularly about the hub section, and vanes extending radially outwardly from the wheel portion. The difference in structure (and the resultant improvement in physical properties) is attributable to the orientation of the grains in the integral casting. Specifically, the grain size in the hub section is made relatively large, the grain in the vanes is relatively fine, and the grain size in the wheel portion is intermediate that of the vanes and the hub portions. In all sections, the grain configuration is substantially equiaxed.

In my parent copending application Ser. No. 378,643, there is described a method for making the improved turbine wheel of the present invention. That method involves positioning a ceramic shell mold or the like on a heat abstracting surface in a furnace enclosure, the mold having communicating molding cavities defining a hub section, a wheel portion extending around said hub section, and vanes extending radially outwardly from the wheel portion. The mold is preheated by means of radiant energy until the walls of the cavities which define the thin wall sections of the casting, -i.e., the walls defining the vane forming cavities, reach a temperature approximating that of the pouring temperature of the metal alloy. Concurrently, a substantial portion of the cavity defining the relatively massive hub is shielded from the radiation to provide a substantial temperature differential between the mold .in the area of the vanes and in the area of the hub. Then, a molten alloy at a temperature not more than about 200 F. above its liquidus temperature is cast into the mold. The hub defining cavity is in open communication with the heat abstracting surface so that the casting is rapidly solidified in the hub defining portion of the mold. The low pouring temperature permitted by this procedure produces a fine equiaxed grain size in the vanes, and the thermal gradients established by the heat abstracting surface produce a casting of exceptional soundness and ductility.

The turbine wheel of the present invention may be composed of any type of metal or alloy, but is preferably composed of a cast superalloy which is essentially a nickel-chromium base alloy. A typical range of composition for such alloys is given in the following table:

Percent Carbon .05 to 0.20. Chromium 8 to 15. Tungsten 3 to 10. Cobalt 8 to 12. Titanium 0.5 to 2. Aluminum 4 to 8. Columbium Up to 3. Boron Up to 0.05. Zirconium Up to 0.20. Nickel Substantially the balance.

The grain structure of the turbine wheel of the present invention is shown by means of photographic reproductions in the figures in which:

FIGURE 1 is a photographic reproduction of a turbine wheel produced according to the present invention, cut away and etched to illustrate the grain configuration;

FIGURE 2 is an enlarged reproduction of the hub portion of the turbine wheel shown in FIGURE 1;

FIGURE 3 is an enlarged reproduction of the wheel portion of the structure shown in FIGURE 1; and

FIGURE 4 is, an enlarged reproduction of the vanes of the turbine wheel.

In FIGURE 1, the relatively massive hub section has been identified at reference character H, the intermediate wheel section by the reference character W, and the vanes by means of reference character V.

From an inspection of FIGURE 2, it will be seen that the grain structure of the hub section H is equiaxed and is otherwise completely sound. The average grain size in the hub section is usually in the range from about A to /2 inch. Not only is the structure metallurgically sound,

. but the physical properties of the hub section are substantially improved over castings from the same alloy made in the conventional manner. For example, the hub section evidences a tensile strength in excess of about 120,- 000 p.s.i., an elongation of at least 8%, and a reduction in area of at least 8%, all measured at room temperature. Specifically, the following table lists the improvements in physical properties which are obtained from castings produced according to the present invention, and those observed in the same alloy cast by conventional casting techniques:

The intermediate wheel portion, as shown in the enlargement of FIGURE 3, has an average grain size which is generally smaller than that appearing in the massive hub portion H. Generally, the wheel portion has a grain size ranging from about /8 to A inch. The photograph of FIGURE 3 is taken in a deeply etched section, and illustrates a complete lack of microporosity in the cast articles.

The vanes, V, as illustrated in FIGURE 4, are a fine, uniformly 'equiaxed grain structure. The average grain size is on the order of about 4 of aninch.

The casting from which the photographs of FIGURES 1 to 4 were taken was an integral turbine wheel of about 12" diameter containing 36 vanes. A ceramic shell mold was employed, and the heat source was a graphite susceptor disposed within an induction coil. Granular magnesia of'about diameter was used to shield the heat abstracting surface and the bottom of the hub portion of the mold. The susceptor was heated to 2400 F. for 14 minutes under a vacuum of about 60 microns, and the mold was filed with a low carbon, nickel-chromium alloy (INCO 7l3-C) at a temperature of about 2500 F.

From the foregoing, it will beunderstood that the turbine wheel of the present invention consists of an integral casting in which the grain size varies with the various portions of the wheel. In all cases, the structure is substantially equiaxed, provided the required soundness and freedom from porosity. The substantial improvement in physical properties of the wheel establish a significant improvement over similar articles of the past.

It should be evident that various modifications can be made to the described embodiments without departing from the scope of the present invention.

I claim as my invention:

1. A turbine wheel com rising an integral casting composed of a relatively massive hub section, a wheel portion extending annularly about said hub section, and vanes extending radially outwardly from said wheel portion, the grain size in said hub section being relatively large, the grain size in said vanes being relatively fine, and the grain size in said wheel portion being intermediate that of the vanes and said hub portion.

2. The turbine wheel of claim 1 in which the average grain size in said hub section is in the range from about A to /2.

3. The turbine wheel of claim 1 in which the average grain size in said wheel portion is in the range from about /8 to A". 1

'4. The turbine Wheel of claim 1 in which the average grain size in said hub section is in the range from about A to /2", the average grain size in said Wheel portion is in the range from about /8 to A, and said vanes consist,

of substantially equiaxed grains of smaller average size than in either said hub section or said Wheel portion.

5. The turbine wheel of claim 1 in which said hub section has a tensile strength in excess'of about 120,000 p.s.i., an elongation of at least 8%, and a reduction in area of at least 8%.

6. The turbine wheel of claim 1 which is composed of a nickel-chromium alloy.

No references cited.

MARTIN P. SCHWADRON, Primary Examiner.

E. A. POWELL, Assistant Examiner. 

1. A TURBINE WHEEL COMPRISING AN INTEGRAL CASTING COMPOSED OF A RELATIVELY MASSIVE HUB SECTION, A WHEEL PORTION EXTENDING ANNULARLY ABOUT SAID HUB SECTION, AND VANES EXTENDING RADIALLY OUTWARDLY FROM SAID WHEEL PORTION, THE GRAIN SIZE IN SAID HUB SECTION BEING RELATIVELY LARGE, THE 